In the atomization of slurries such inserts are inserted into the atomizer wheel in order to guide the slurry feed out of the atomizer for forming droplets for the further drying and/or absorption process. During atomization, the internal structures of the atomizer wheel, including the inserts, are exposed to wear which, depending on the slurry to be atomized, may even be very heavy. However, this wear is normally restricted to certain well-defined areas of the atomizer wheel or inserts.
In general, the wear on different parts of the atomizer wheel arises during rotation of the wheel, where owing to the centrifugal forces and the nature of the feed, the feed affects the internal parts with a force that causes heavy abrasion. Parts exposed to abrasion from feed are therefore made abrasion-resistant and replaceable.
A series of improvements have been suggested in order to enhance the abrasion-resisting properties of the internal structures of the atomizer wheel, in order to prevent the ongoing deformation and possibly fracture, e.g. as disclosed in U.S. Pat. Nos. 3,640,467 and 4,684,065 (Niro).
Disclosed in both documents are inwards-protruding inserts which ensure that a layer of liquid will deposit on the internal wall of the wheel during the rotation and hereby prevent wear. Owing to the centrifugal forces the heavier parts of the layer, i.e. the suspended solid material, is separated from the liquid in the layer and deposited directly on the wall so as to fill the area surrounding the inwardly extending portions of the inserts. In this way the inner surface of the wheel rim is protected against abrasion from the feed, since during operation a layer of feed solids will settle on the inside wall to a thickness determined by the length of the protrusion, consequently the abrasion will take place on the sedimented layer itself and not on the inside wall of the wheel.
However, it has turned out that these inserts during atomization of some abrasive slurries experience extremely high wear on the foremost parts, seen in the tangential or rotational direction, which has entailed that not only the wear-resistant lining but also the steel bushing show sign of wear. It is believed that this effect is due to the fact that whirl formation prevents the formation of a protective layer locally at the front end of the inserts.
Further improvement of these inserts has therefore been developed for e.g. disclosed in European patent No. EP 1 184 081 B1 (Niro), where each insert is provided with a transition surface in the inwards protruding part of the insert, thereby directing the flow of the feed along the transition surface to the inner side of the external wall thereby avoiding wear on the bushing. It is believed that the wear on the bushings in this way is limited since the whirl formed in front of the insert is controllably led past the front of the insert, during rotation to form a coherent layer of protective material on the inner side of the external wall.
In the prior art, it has furthermore been suggested to mount the inserts so that they can be turned, as they are gradually being worn, in order to increase their overall lifetime. However, turning of the inserts requires that the apparatus is shut down. The need to frequently turn the inserts results in manufacturing stops, which are time-consuming and costly due to time periods without any manufacturing. Furthermore, in order to meet demands set in for instance environmental regulations, start-and-stop and downtime should generally be reduced to a minimum.